Data and Code for: Clean Identification? The Effects of the Clean Air Act on Air Pollution, Exposure Disparities and House Prices

We assess the US Clean Air Act standards for fine particulate matter (PM2.5). Using high-resolution data, we find that the 2005 regulation reduced PM2.5 levels by 0.4μg/m^3 over five years, with larger effects in more polluted areas. Standard difference-in-differences overstates these effects by a factor of three because time trends differ by baseline pollution, a bias we overcome with three alternative approaches. We show that the regulation contributed to narrowing Urban-Rural and Black-White PM2.5 exposure disparities, but less than difference-in-differences suggest. Pollution damages capitalized into house prices, on the other hand, appear larger than previously thought when leveraging regulatory variation.

本研究评估美国《清洁空气法案》（Clean Air Act）针对细颗粒物（PM2.5）制定的排放标准。借助高分辨率数据开展分析后，我们发现2005年出台的该项法规在五年内将PM2.5浓度降低了0.4微克/立方米，且在污染更为严重的地区，政策减排效果更为显著。由于不同基线污染水平对应的时间趋势存在差异，标准双重差分法（difference-in-differences）会将该政策的减排效应高估三倍；针对这一偏误，我们采用三种替代分析方法予以修正。研究表明，该项法规有助于缩小城乡以及黑人群体与白人群体之间的PM2.5暴露差距，但该效应的实际幅度小于双重差分法估算的结果。另一方面，当借助政策变异开展分析时，房价中所资本化的污染损失规模似乎比此前学界的认知更大。